Study On The Difference Between Valleys And Slopes Vegetation Succession Of Burned Area In The Great Khingan Mountains

Forest ecosystem is an important part of the terrestrial ecosystem,with complicated structure and abundant resources.It plays an important role in preserving ecological balance,regulating climate and conserving water and soil.The Greater Khingan Mountains are a major green ecological barrier in northern China,the largest forestry base,and also an important material base for economic and social development.Wildfires are one of the most natural disturbances of the forest ecosystem and cause severe destruction to the forest ecosystem.Postfire vegetation succession is the only way to enhance the species structure,function and productivity of forest ecosystems.It’s important to study the dynamic process of post-fire vegetation succession for forest management and scientific decision-making.In this paper,ten burned areas in the Greater Khingan Mountains from 1986-2010 were selected by combining remote sensing technology and field survey to study the dynamic process of vegetation succession after the fire.Based on the remote sensing data,this paper analyzes the characteristics of EVI(Enhanced Vegetation Index)variation in burned areas under the conditions of burned and unburned,different terrain and different fire intensity.Based on the field investigation data,use the space–time substitution method,this paper analyzes the changes of species and species diversity in the burned area,and constructs the vegetation succession sequences of valleys and slopes.The specific conclusions of this paper are as follows:(1)After 9-12 years postfire,the EVI of burned area can reach the pre-fire state.The EVI growth rate of burned areas under different terrains is as follows: slopes > valleys.The EVI growth rate of burned areas under different fire intensity is as follows: high intensity > moderate intensity > low intensity.This indicates that the difference between topography and fire intensity can affect vegetation succession.(2)With increasing time,the richness of species showed a trend of gradual decline on valleys and slopes,and the high frequency of shrub species showed a gradual increasing trend.The final stage of the valleys and the slopes,a mixed forest of larch and birch formed,accompanied by some low shrubs.(3)After fire disturbance,the species diversity showed an overall trend of initially increasing and then decreasing trend.Seventeen years postfire was the cutoff point in species richness and diversity changes in valleys and slopes.Initially,the species richness and species diversity of valleys were higher than those of slopes,but after 17 years,the richness of species in the valleys were the same as that on the slopes,the diversity of species on the slopes were higher than that valleys.(4)From 11 years to 35 years postfire,shrub species composition changes are characterized by shade-tolerant shrubs appear or increase,light-demanding shrub gradually reduce or disappear.The species composition of trees showed that larch,birch and aspen appeared in the middle and late stage of postfire successsion in the valleys,while those had grown in the early stage of post-fire successsion on the slopes.With increasing successsion time,a stable mixed forest of larch and birch gradually succeeded.(5)Significant differences in vegetation succession sequences between valleys and slopes at the beginning of succession.The sequence of the vegetation succession in valleys: In the early stage,tall shrubs dominated;In the middle stage,larch,birch,aspen and some shrubs;in the final stage,mature coniferous broad-leaved mixed forest dominated by larch and birch with a few low shrubs.The succession sequence of slopes is follows: In the early stage,immature larch forest and a few low shrubs;In the middle stage,the tree layer dominated by larch,birch and aspen and the understory shrubs were abundant;in the finally stage,the mature mixed forest was accompanied by some low shrubs.